The present invention relates to an insulating gate field effect semiconductor device and a method of manufacturing the same, and more specifically to an insulating gate semiconductor device which can be fabricated by a low temperature process and a method of manufacturing the same.
In recent years, fabrication of semiconductor devices with thin film transistors (TFT) provided on a large area of low cost glass substrate are required in order to reduce the cost of display devices, image sensors or the like. When the glass substrate is used, a low temperature process of approximately 600.degree. C. is needed to prevent softening of the glass substrate.
For example, when a polysilicon or amorphous silicon layer is used as a channel semiconductor film and a silicon dioxide(SiO.sub.2) film as a gate insulator film for the TFT, in order to keep the heat treatment temperature for fabricating the TFT below 600.degree. C., the following deposition techniques are employed due to possibility of a low temperature deposition of SiO.sub.2 film as a gate insulator film. The deposition techniques are piling techniques like plasma chemical vapor deposition (CVD) (for example, refer to Journal of Applied Physics Vol.60(9) p3,136 (1986)), remote plasma CVD (for example, refer to Journal of Vacuum Science Technology A5(4) p2,231 (1987)), AP(Atmospheric Pressure) CVD, LP(Low Pressure) CVD, sputtering (for example, refer to IEEE Trans. Electron Devices 135(12) p3104 (1989)) or the like.
By using these film deposition techniques, however, a dense SiO.sub.2 film is difficult to obtain. Accordingly, to densify the deposited SiO.sub.2 film, a high temperature annealing at approximately 900.degree. C. or a lamp annealing in a nitrogen ambient is considered. That is, to form a high quality gate insulator film by any technique, a heat treatment at a temperature higher than 600.degree. C. is considered necessary. The above described SiO.sub.2 film is not so dense and becomes hygroscopic after the succeeding process, especially after the densifying anneal at a temperature of approximately 600.degree. C., degrading the characteristics and lowering reliability of the TFT.
In deposition of a SiO.sub.2 film by plasma CVD, introduction of a gas including fluorine together with an organosilane and oxidizing gas is disclosed (Japanese Unexamined Patent Publication JP-A 7-90589(1995)). To improve the film property, however, control of fluorine content in the oxide film to a constant value is required, and therefore some special apparatus is needed.
As described above, a high quality gate insulator film can be obtained at a relatively high deposition temperature. Application of a glass substrate for film deposition, however, requires a low temperature process of approximately 600.degree. C. On the other hand, when a gate insulator film is deposited at a temperature lower than 600.degree. C., a dense and high quality film could not be obtained. Because the film adsorbs moisture after the succeeding process, high level of traps are introduced to the gate insulator film and channel interface giving a harmful influence to the TFT characteristics. These traps cause injection of hot electrons and reliability problems to the device.